First Preclinical Imaging of Primary Cartilage Neoplasm and Its Local Recurrence Using 99mTc-NTP 15-5 Radiotracer

This study on a rat model of grade II chondrosarcoma aimed to determine whether the radiotracer N-(triethylammonium)-3-propyl-[15]ane-N5 radiolabeled with 99mTc (99mTc-NTP 15-5), which binds to cartilage proteoglycans, has pathophysiologic validity for in vivo imaging of cartilage tumoral tissue. Methods: We used 2 experimental approaches with the Swarm chondrosarcoma rat model: that is, a primary paratibial location and local recurrence after intralesional curettage. 99mTc-NTP 15-5 scintigraphy and 99mTc-hydroxymethylenediphosphonate (99mTc-HMDP) scanning were performed at regular intervals during 50 d after tumor implantation in a paratibial location (primary model; n = 12 animals) and after intralesional curettage in a femoral condyle location (recurrence model; n = 9 animals). For each animal, positive scans were analyzed at each time point using the target-to-background ratio (TBR), with the target region of interest delineated over the tumor and the background region of interest over muscle. In each model, the TBR time course was followed against primary tumoral growth or recurrence. Tumor volume was monitored for 2 mo by measuring the 2 perpendicular diameters. At study end, animals were sacrificed for histopathologic analysis. Results: For both models, 99mTc-NTP 15-5 scans showed tracer accumulation at the site of implantation or curettage. For the primary tumor model, the mean TBR was 1.6 ± 0.14 by day 4 after implantation and increased over time as the disease progressed, with a mean TBR of 4.25 ± 0.25 on day 45. For the recurrence model, mean TBR was 3.27 ± 0.24 by day 4 after curettage and increased with recurrence, with a mean value of 5.25 ± 0.49 on day 50. 99mTc-HMDP bone scans were negative for both models throughout the study; at a later stage of the study, an area of 99mTc-HMDP accumulation was seen in the diaphysis of the bone adjacent to the tumor and was attributed to remodeling. Conclusion: These experimental results in 2 preclinical models of grade II chondrosarcoma bring forward data in favor of 99mTc-NTP 15-5 radiotracer for imaging primary growth of chondrosarcoma and its local recurrence after surgery.